cobalt oxide slip on earthen ware

So I fired six earthenware tiles which had been coated in cobalt oxide slip. Three of the tiles were lower down in the kiln than the other three. Now the lower down ones are very intense lovely blue and the slightly higher ones are slightly less blue. I fired these to 1000C with a soak of half an hour. They are for a house sign, so in effect they now dont match. Is it worth firing them again but reversing the positions to see if that helps. I just love ceramics! arrrgggg..... any suggestions appreciated. T

I like them, too, but see the problem and think they would look better if all were the darker blue. I think it would be well worth the re-fire but since you say the darker blue were on the bottom that may mean they were slightly cooler instead of hotter which may make re-firing a waste of time since you can fire the pale ones hotter but not cooler. Does it look like to you that the pale tiles got hotter? Good luck.

One of the things I have learned over a long period id is color is SUPER important (that is it all needs to match . You should fire them all together in same spot.
This is especially true in high fire reduction and as you just found out matters at lower temps to some degree.-I still like the work but if you want it all the same then make it all over and fire all together same shelve area.
Mark

So. That made no difference what so ever. I cut some new tiles this morning and will re do them this week. oh well serious eye rolling going on! T

I was afraid that would happen. You probably have a better chance of making the darker ones lighter than the other way around. Good luck with the new tiles.

Jim

I was trying to fire higher to turn the darker ones lighter..... did i mention that I am ceramically challenged so i will need luck!!! I have never ever had this happen with my colbalt slip not EVER! /> ps I almost wanted to positive rate you on that comment, to see what it takes to get out of a neutral rating.... anyway thanks again T

I just looked at your profile, someone must have the hots for you....Good.... Holy smokes!

One of the things I have learned over a long period id is color is SUPER important (that is it all needs to match . You should fire them all together in same spot.This is especially true in high fire reduction and as you just found out matters at lower temps to some degree.-I still like the work but if you want it all the same then make it all over and fire all together same shelve area.Mark

Thanks Mark, they were only about two inches lower than the other ones. I have a feeling that the slip was a bit too wet and that somehow affected things, You know when you try to think about the process and if anything changed, well I vaguely remember like a slight cobalt scum floating on the surface of the pale. Oh well, just one of those things. Thanks for your comment anyway. T